To facilitate the healing of wounds, the wound environment needs to be conducive to cell survival and proliferation. If the wound becomes dehydrated or if a pool of exudate develops above or within the wound, oxygen diffusion to or through the wound becomes impeded and the cells become hypoxic, which impairs their function (for example, the antimicrobial activity of neutrophils or the production of collagen by fibroblasts). Under sustained hypoxic or anoxic conditions the cells may die. This is especially true if the wound has impaired vascular delivery of oxygen from the native blood vessels. Dressings which are used to simply cover wounds typically absorb at least a thin layer of exudate (e.g., more than a couple hundred microns of exudate within the dressing). If the exudate and/or if the dressing material itself limits oxygen permeation to the wound, the covered cells may die and impede wound healing. As the cells die, they release cytotoxic factors which cause additional cells to die, potentially leading to a downward spiral of cell death.
Wound dressings generally cover a wound and limit dehydration but also restrict oxygen availability to the wound, which leads to cells becoming anoxic and dying due to the limited oxygen supply. Cellular preparations such as platelet rich plasma gels improve wound healing, and providing oxygen from outside the wound may improve their effectiveness.
For aggressively weeping wounds, dressings used sometimes rely on evaporation to remove excess water from the exudate and wound site; however, this has the undesirable effect of concentrating toxic factors (e.g., metalloproteases) in the exudate and may worsen conditions. Moreover, excess evaporation may also lead to wound dehydration which may further worsen the environment for wound healing. Dried exudate can form a crust with abrasive properties, further impeding healing.
In some treatments, wet gauze or hydrogel dressings are used to maintain a moist wound environment. In other situations hyperbaric oxygen treatments are used to oxygenate wounds. Other treatments for oxygenating wounds have used glucose and glucose oxidase to generate oxygen in situ or electrolysis of water in situ to generate oxygen. Other designs have actively delivered oxygen gas via a cannula under conventional dressings.
Yet other treatments have delivered peroxide rather than oxygen to wound sites where the peroxide is converted to oxygen in situ by native catalase or by, e.g., manganese dioxide.
Additional treatments have utilized films as dressings, e.g., polyurethane films, which include a stored reservoir of oxygen for application to the wound. Such reservoirs require replenishment. Absorbent materials such as polyHEMA hydrogel beads are sometimes poured directly into a wound. Foreign materials poured into a wound may trap layers of exudate, water, or debris after becoming saturated, limiting oxygen diffusion through the interstitial spaces. Moreover, depending on the molecular weight exclusion profile of the absorbent material, debris and toxic high molecular weight constituents of the exudate may become concentrated as water is absorbed into the material.
Accordingly, there is a need for a wound dressing which is able to maintain consistent high levels of oxygen permeability, prevent dehydration, and accommodate potentially copious volumes of exudate.